In the long term I want to understand the molecular basis of the heritable forms of combined pituitary hormone deficiency, a disorder usually due to the lack of several anterior pituitary cell types. Recently a candidate gene, Prophet of Pit-1 (prop-1) encoding a homeodomain transcription factor, was cloned by the sponsor's laboratory. A point mutation in the homeodomain of Prop-1 found in Ames mice can still bind to Prop-1 consensus sites. To fully understand the role of Prop-1 in pituitary cell lineage determination, the following specific objectives are proposed: Aim1: To generate mice deficient in Prop-1, to determine pituitary hormone deficiency phenotypes. I will also knock-in a B-lacatamase (beta- lac) reporter gene into the locus simultaneously, so that I can purify the Prop-1 expressing cells using fluorescence activated cell sorting (FACS) technique; Aim2: To identify Prop-1 target genes using representational difference analysis (RDA), a PCR-based subtractive hybridization strategy allowing identification of transcripts that exhibit 10-fold or greater differences in their concentrations between two different sources; Aim3: to rescue depleted Pit-1 dependent cell lineages in the Prop-1 mutant by knock-in of Pit-1 into the Prop-1 locus through homologous recombination.